This invention pertains generally to die cutting. More specifically this invention relates to anvil structure for use in conjunction with die cutting apparatus, the anvil structure defining a reaction surface for the cutting rules of die cutting structure.
Rotary die cutting pertains to the art of cutting a moving workpiece, e.g. a continuously moving web or a sheet of material, without interrupting the movements of the workpiece. In typical applications, moving webs or sheets of material such as cardboard and corrugated paperboard, are passed between a cutting roller and an anvil roller. Cutting elements known as cutting rules are mounted on the cutting roller for rotation therewith. The anvil roller is provided with a cylindrical cover known as a cutting die blanket which fits around the surface of the anvil roller and effectively increases its diameter by twice the blanket thickness. The axes of rotation of the cutting roller and the anvil roller are parallel and displaced by an amount such that at their points of closest proximity the cutting rules penetrate the surface of the die blanket.
As the cutting rules penetrate the surface of the die blanket, a resistance to the penetration is developed which, for purposes of this application, is called a reaction force. Adjustment of the relative positions of the axes of rotation of the cutting die roller and the anvil roller is made to provide a degree of penetration and therewith a degree of reaction force sufficient to insure complete cutting of the moving web or sheet of material.
Over the years those concerned with the design, construction and operation of rotary die cutting apparatus have devised varied approaches to avoid having the cutting rules strike the die blanket repetitively at the same location. Such repetitive striking causes excessive blanket wear at the location of the strike with virtually no wear at other locations on the blanket surface.
In some conventional die cutting apparatus the shafts of the cutting roller and the anvil roller are mechanically inter-engaged through a gearing pair. The gear of the anvil roller shaft may have one less tooth than the gear of the cutting roller shaft or, for the same purpose as is discussed below, the diameters of the rollers may be slightly different. The purpose of such structure is to create a difference in the circumferential velocity of rotation of the cutting and anvil rollers so that the cutting rules do not strike repetitively the same locations on the die blanket surface. Rather, the disparity in rotation permits the cutting rules to strike a different location on the surface of the blanket at each successive rotation thus prolonging the life of the cutting blanket.
In those die cutting apparatus wherein different degrees of circumferential velocity between the anvil roller and the cutting roller are not permissible, e.g. adaptation of printer-slotter apparatus to perform a die cutting function, various approachs have been taken to preclude repetitive striking of the die blanket by the cutter rule. One of these has been to provide sliding anvil blankets. Such an approach is disclosed in U.S. Pat. No. 3,282,142 issued for an ANVIL FOR ROTARY DIE CUTTING, U.S. Pat. No. 3,522,754 issued for a REINFORCED FREE WHEELING RESILIENT COVER FOR ROTARY DIE CUTTING ANVIL, and in U.S. Pat. No. 3,274,873 issued for a ROTARY ANVIL CONSTRUCTION.
Another approach to solving the problem of repetitive striking of the die blanket at the same location is found in my U.S. Pat. No. 4,073,208 for an ANVIL STRUCTURE FOR ROTARY DIE CUTTING APPARATUS. The structure disclosed in this patent embodies a die blanket rigidly mounted on a slip bearing which is mounted on the anvil head.
Although my pateneted anvil structure solved many of the problems presented by prior approaches, the relative displacement it provided was in a single direction, i.e. linearly around the surface of the anvil head. Thus, in applications where the cuts are relatively long and linearly oriented in the direction of passage of the workpiece between the cutting roller and the anvil roller, prior art structures may reduce repetitive striking at the same location on the die blanket, but large areas of the die blanket surface remain untouched by the time the anvil structure must be reconstructed by replacement of the blanket.
Needless to say, the failure to utilize larger areas of the die blanket surface results in more frequent reconstruction of the anvil structure by replacement of the blanket with attendant machine down time. Thus, any structure which increases use of die blanket surface while minimizing repetitive striking of the blanket surface at the same location is highly desirable.